This invention relates to a digitizer stylus assembly and, more particularly, to such an assembly in which contact with, and pressure exerted on, a writing surface is sensed and measured for use in connection with portable computing devices, or the like.
As computers become smaller and more portable, small hand-held computers, such as "pen" or "pad" computers, have evolved which enable the user to "write" on the computer by applying an active digitizer stylus, which is part of a digitizing subassembly, to a digitized surface on the face or screen of the pad or tablet.
In these arrangements, is often important to detect the status of the stylus relative to the surface and, more particularly, whether or not the stylus is engaging the surface preparatory to initiating the writing. Also, some software responds to different pressures exerted on the stylus as a result of pressing the stylus on the surface to perform various functions, such as to detect handwriting, change images on the screen, etc.
Some prior assemblies that utilize pressure sensing for active styli in this art incorporate a switch in the stylus tip to detect stylus contact with the digitizer surface. However, these switches are used only to detect stylus contact but cannot measure stylus tip pressure.
Other assemblies of this type utilize a force sensing resistor device associated with the stylus to measure pressure. However, these devices suffer from wide variations in their accuracy and do not allow for accurate control of the pressure range, linearity, sensitivity and granularity.